Oil pressure gauge

[stasiu]

Hello,

The oil pressure gauge is still not working in my 03 c2 after replacement of the sending unit. Few weeks ago the gauge started go going in and out - showing correct pressure, then dropping to 0, then correct pressure and so on... Recently it stopped showing anything and stays at 0, so I replaced the sending unit, but it didnt help.

Now i'm guessing there's a short somewhere in a wiring, but need help troubleshooting it.

Here's what I know so far:

-resistance values are completely out of range of expected values

-there is continuity on both wires from sender unit to the instrument cluster

-I measured voltage at the plug behind drivers seat and here are the values: Ignition off: +5V, ignition on: -7V, engine on: -9V. This makes me think that when the ignition is on, it causes 12/14V to flow in the opposite direction to the +5V.

-I have piwis scanner and tested the instrument cluster - gauge works

Any ideas on how to troubleshoot it further? Seems to me that there must be a short somewhere between instrument cluster and the plug behind driver's seat. Does anybody know if the voltage is supposed to stay at 5V at all times?

Thanks,

Patrick

[Ahsai]

The sensor has a varaible resistor (varies with pressure) and a switch inside. What resistance value you get between the "G" pin and the metal casing of the sensor? It sould be ~10 ohms at 0 pressure and 180 ohm, at 5 bar.

You can use a resistor (or potentiometer) with value in between 10 and 180 ohm to substitue the sensor and see if the gauge moves.

Not sure how you get negative voltage. Did you measure all the voltage with respect to the chassis ground?

[Ahsai]

If you become a contributing member, you can access this document that explains how the DME and the sensors work. It mentions the 5v reference for sensors.

http://www.renntech.org/forums/files/download/1660-after-sales-training-advanced-engine-management-systemspdf/

[stasiu]

The sensor has a varaible resistor (varies with pressure) and a switch inside. What resistance value you get between the "G" pin and the metal casing of the sensor? It sould be ~10 ohms at 0 pressure and 180 ohm, at 5 bar.

You can use a resistor (or potentiometer) with value in between 10 and 180 ohm to substitue the sensor and see if the gauge moves.

Not sure how you get negative voltage. Did you measure all the voltage with respect to the chassis ground?

Ahsai,

 

Thank you for that information. I checked the resistance between G pin and the metal casing and it's correct with engine on and off. I get the same resistance on the plug that connects to the instrument cluster. What does the 2nd wire (green/white) that goes to the sensor do? With ignition off it has continuity to ground, with ingition on there's no continuity, no voltage and no resistance.

 

[EDIT] I found the info about the green/white wire - it's emergency contact

Edited July 3, 2014 by stasiu